Alignment method, overlay deviation inspection method and photomask

ABSTRACT

When an alignment mark and first and second overlay deviation inspection marks as well as a device pattern are successively formed on a wafer using a first photomask and a second photomask, each of the alignment mark and the overlay deviation inspection marks are formed to have a part of the device pattern or marks having sizes and shapes similar to those of the device pattern, whereby these marks receive a deviation error caused by the influence given by the aberration of the light projection optical lens used for performing the pattern transfer and an error in the following processing steps in substantially the same degree as the device pattern, and an amount of the overlay deviation error is measured correctly so as to achieve an alignment of the photomasks in a high accuracy.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-172077, filed Jun.8, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an alignment method forprecisely overlaying photomasks used in lithography steps performed inmanufacturing of semiconductor devices, a pattern-overlay inspectionmethod, and a photomask used in these methods.

[0003] In the conventional method of manufacturing a semiconductordevice, a semiconductor wafer is exposed to lights having mask patternsexceeding 20 patterns to overlay the mask patterns successively on thesemiconductor wafer for forming finally a plurality of device patternson the semiconductor wafer. When the pattern exposure is performed, thepositioning of a photomask in an exposure apparatus is performedaccording to an alignment mark formed in advance on the photomask. Afterthe positioning is fixed, the pattern exposure is performed to form aresist pattern on a chip of the semiconductor wafer for correctlyoverlaying the resist pattern on a pattern formed in advance within thechip.

[0004] The pattern-overlay inspection is then performed on the basis ofthe resist pattern and the pattern formed in advance on the chip so asto inspect whether a device pattern to be formed is correctly overlaidon the device pattern formed in advance on the chip.

[0005] It was customary in the past to inspect the overlay deviation ofthe alignment by forming inspection marks with given sizes and shapesfor inspecting the overlay deviation of the alignment on first andsecond layers of wires, for example, on a silicon wafer. Then the formedmarks are used in the measuring step for obtaining the deviation amountof the relative positions of the overlay inspection marks with aninspecting apparatus. In this case, since the inspection marks forinspecting the overlay deviation of the alignment were designed to havea size and shape that could be easily recognized by the inspectingapparatus, it was customary in the past to use the particular markdiffering from the device pattern in size and shape.

[0006]FIG. 8 is a plan view showing typical conventional inspectionmarks for inspecting the deviation of alignment formed on the wafertogether with a device pattern. The inspection marks include inner fourmarks 101 and outer four marks 102. The outer marks 102 are arranged tohave a pitch of 28 μm as shown in the figure. Therefore, each of theouter marks 102 has a length slightly shorter than 28 μm.

[0007] The inspection marks 101 are formed in advance in the first layerof wires on the wafer, for example, and the inspection marks 102 arethen formed on a second layer of wires on the first layer of wires tohave an arrangement as shown in FIG. 8. The deviation of alignment canbe inspected by obtaining a subtraction of a measured distance betweenthe neighboring marks 101 and 102 and a reference distance, for example.

[0008] However, with progress in miniaturization of the device patternachieved in recent years, a difficulty has arisen that, in the casewhere an inspection mark for inspecting the deviation of alignment and adevice pattern are formed simultaneously, it is substantially impossibleto form both the inspection mark and the device pattern withsubstantially the same degree of accuracy.

[0009] The difficulty is derived from the situation that the inspectionmarks for inspecting the deviation of alignment and the device patternare not similar or equal to each other in size and shape. To be morespecific, an error in the pattern position, size and shape takes placedue to the aberration and focus position of the projection opticalsystem including a projection lens in the exposure apparatus used in thelithography. In addition, the degree of the error varies depending onthe shape, size and local density of the inspection marks and those ofthe device patterns.

[0010] It should also be noted that the working processes such as theetching and CMP (Chemical Mechanical Polishing) processes are likely toaffect the degree of the error by the difference in the pattern shapeand the difference in the local density of the patterns. FIG. 9exemplifies a device pattern formed on the wafer together with theoverlay deviation inspection marks shown in FIG. 8, for example. Asshown in FIG. 9, the pitch of the device pattern is 0.35 μm. Thus, thedevice pattern shown in FIG. 9 is utterly different from the inspectionmarks shown in FIG. 8 in shape and size.

[0011] Also, the device pattern includes in some cases patternsdiffering from each other in the shape, size, density, etc. even ifthese patterns are formed on the same layer of wires on the wafer. Insuch a case, a difference in the error amount in respect of the patternposition and shape takes place depending on the difference in thepattern size and shape. In order to form a precise pattern, it isdesirable to measure the errors in the position, shape and size of allthe device patterns. However, such a measuring means has not beendeveloped in the past.

[0012] The similar problems are also generated in the alignment markused for finding the alignment position of the photo-mask in the lightexposure step performed by using the exposure apparatus as well as inthe inspection mark for measuring the deviation of alignment. In thecase of using a mark that does not resemble the device pattern as thealignment mark, a difficulty is generated that it is difficult torecognize correctly the actual device pattern position on the waferexposed to the light.

[0013]FIG. 10 is a plan view showing the conventional alignment markformed on a wafer. The conventional alignment mark has a pattern havinga pitch of 12 μm larger than that of the device pattern shown in FIG. 9and is shaped like an oblong band, which widely differs from the devicepattern shown in FIG. 9 in shape, size, etc.

[0014] Jpn. Pat. Appln. KOKAI No. 9-102457 discloses a means for solvingthe problem of an error generated from the situation that the alignmentmark differs from the device pattern in shape and size. It is disclosedthat the length of the alignment mark is divided into a length close tothat of the device pattern. However, since the mark for inspecting thedeviation of alignment and the alignment mark are designed separatelyfrom each other in the past, the inspecting mark and the alignment markwidely differ from each other in, for example, the pitch as apparentfrom FIGS. 8 and 10, resulting in failure to permit these inspectingmark and the alignment mark to be related to each other in the patternsize and shape.

[0015] This implies that the degree of the error in the pattern positiontaking place in the lithography and the subsequent working steps differsdepending on the mark. As a result, it was difficult to measureaccurately where and in what shape the device pattern formed on thebasis of the alignment mark was formed so as to cause generation of thedevice pattern error.

[0016] As described above, the alignment mark, the mark for inspectingthe deviation of alignment, and the device pattern differ from eachother in the constituents of the pattern such as the pattern shape, sizeand density, with the result that the degrees of errors taking place inthe pattern forming step differ from each other. For example, in forminga multi-layer structure by successively overlaying a first layer ofwires, a second layer or wires, etc. on the wafer, it is difficult tooverlay these layers of wires one upon the other with a high accuracy,thereby giving rise to a serious problem to be solved for manufacturinga semiconductor device of a multi-layer structure.

[0017] An object of the present invention is to provide an alignmentmethod, a high accuracy overlay inspection method and a photomask usedin these methods, in which both the alignment mark and the devicepattern are formed so as to be affected in substantially the same degreeby the error caused by the aberration of the projection optical systemof the light exposure device used in exposing the pattern to theexposure light and by the error in the processing.

[0018] As a result, the amount of the positional deviation of the devicepattern is rendered substantially equal to the amount of the positionaldeviation of the alignment mark and the mark for inspecting the overlayof photomasks.

[0019] According to the present invention, an alignment method that isexpected to achieve the alignment with a high accuracy, an inspectingmethod of overlay of device patterns in a high accuracy, and a photomaskused for these methods.

BRIEF SUMMARY OF THE INVENTION

[0020] The present invention is featured in that, where a firstphotomask and a second photomask are used in the lithography stepemployed in the manufacturing process of a semiconductor device, themark for inspecting the deviation of the alignment of the mask and thealignment mark are constructed to include at least a part of the devicepattern included in these masks when the first or second photomask isused for the light exposure. Since each of the alignment mark and themark for inspecting the overlay of device pattern includes a mark equalor similar to those of the device pattern in size and shape in thecorresponding photomask, the error caused by the aberration of theprojection optical system used in the pattern exposure step and theerror in the processing are received in substantially the same amount.As a result, the amounts of the positional deviation of these marks andpatterns are substantially the same so as to make it possible to expectan alignment of a high accuracy.

[0021] The present invention is also featured in that, where a firstphotomask and a second photomask are used in the lithography stepincluded in the manufacturing process of a semiconductor device, markscapable of measuring the relative deviation amount taking place amongdifferent patterns in size and shape are formed in the first photomaskas the marks for the overlay inspection of the device patterns. Themarks capable of measuring the relative deviation amount among thedifferent patterns include a reference pattern having a relatively smalldeviation with respect to that of the device pattern shape and a markhaving a relatively large deviation with respect to the device patternshape.

[0022] The second photomask has also overlay inspection marks capable ofmeasuring the amount of the relative deviation among different patterns,the relative deviation taking place when the second photomask is usedfor the light exposure. The marks include a reference mark having arelatively small deviation with respect to that of the device patternshape and a mark having a relatively large deviation with respect to thedevice pattern shape, in the same manner as the first photomask.

[0023] Since the amounts of the positional deviation of the firstphotomask and the second photomask, the positional deviation beingcaused by the aberration of the projection optical system of the devicepattern, are measured, and the result of the measurement is used forcorrecting the position in performing the light exposure by using thefirst photomask and the second photomask which are overlaid one upon theother, it is possible to expect the alignment of a high accuracy.

[0024] Further, the present invention is featured in that, where a firstphotomask and a second photomask are used in the lithography stepincluded in the manufacturing process of a semiconductor device, thereference patterns of the first and second masks are the patternsreceiving substantially the same error even if there is an error in theaberration of the projection optical system. When the light exposure isperformed by overlaying the second photomask on the pattern formed bythe first photomask, the overlay is corrected in view of the error inthe relative positional deviation of the device shape relative to thereference pattern of the first photomask and in view of the similarerror of the second photomask, making it possible to obtain a desiredoverlaying accuracy.

[0025] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0026] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0027]FIGS. 1A to 1C are plan views collectively showing an alignmentmark and a mark for inspecting the deviation of pattern overlay, whichare formed in the light exposure step performed by using first andsecond photomasks by the method of the present invention, and a chipformed by using these alignment mark and inspecting mark as well as theprocedure of the light exposure treatment;

[0028]FIGS. 2A to 2D are plan views collectively showing variousexamples of alignment marks of the present invention formed bycombination of different patterns on the same mask;

[0029]FIGS. 3A to 3C are plan views collectively exemplifying marks forinspecting the deviation of alignment, which are formed by the patterntransfer or pattern exposure of the present invention;

[0030]FIG. 4 is a plan view showing another example of the alignmentmark of the present invention formed by combination of differentpatterns on the same photomask;

[0031]FIGS. 5A and 5B are plan views collectively showing other examplesof the marks of the present invention for inspecting the deviation ofalignment, which are formed by combination of different patterns on thesame photomask;

[0032]FIGS. 6A to 6E are cross sectional views collectively showingsequentially steps of a manufacturing method of a semiconductor deviceby employing the alignment method of the present invention;

[0033]FIG. 7 is a plan view showing a wafer using the alignment methodof the present invention;

[0034]FIG. 8 is a plan view showing a conventional mark for inspectingthe deviation of alignment;

[0035]FIG. 9 is a plan view showing one example of a device patternformed on a wafer; and

[0036]FIG. 10 is a plan view showing the conventional alignment mark.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Embodiments of the present invention will now be described withreference to the accompanying drawings. In the present invention, wherethe light exposure is performed by using a first photomask and a secondphotomask in the lithography step included in the manufacturing processof a semiconductor device, the mark for inspecting the deviation ofoverlay and the alignment mark included in each of these photomasks areconstructed to include at least a part of the device pattern shapeincluded in the mask.

[0038] A first embodiment of the present invention will now be describedwith reference to FIGS. 1A to 1C. Specifically, FIGS. 1A to 1Cschematically show the state that, when a device pattern portion 4 ofFIG. 1B is formed on a chip 11 by exposing a wafer 1 to light by usingfirst and second photomasks, an alignment mark and an inspecting markare formed simultaneously, and that these marks and the device patternare formed on the chip 11 in positions deviated by predetermined amountsfrom an ideal positions.

[0039] In the first step, the device pattern portion 4 is formed byusing a first photomask 21 in a predetermined position on each of aplurality of chips 11 formed on the wafer 1 shown in, for example, FIG.7, e.g., in the position shown in FIG. 1B together with an alignmentmark portion 25B and a mark portion 5B for inspecting the deviation ofoverlay.

[0040] Concerning the alignment mark portion 25B, a mask pattern 25Aconsisting of a mask substrate 23 of a glass plate and a light shieldingfilm 24 of a predetermined pattern formed on the mask substrate 23 isformed on the photomask 21, as shown in FIG. 1A.

[0041] Light emitted from a light source (not shown) is incident on thefirst photomask 21 from the upper surface of the mask substrate 23 andpasses through the light shielding film 24 so as to form a patternedlight of the alignment mark. The patterned light is converged by aprojection lens 3 so as to be projected as an alignment mark 41 withinthe alignment mark portion 25B on a resist film 21A formed on the wafer1.

[0042] As described herein later, if an ideal pattern forming position,when the positional deviation amount of the mask pattern 25A is zero, isdenoted by broken lines, the alignment mark 41 exposed to light isdeviated in the X-direction in an amount of X1. To be more specific, ifthe resist 21A on the wafer 1 is exposed to light by using the firstphotomask 21, the alignment mark 25A within the alignment mark portion25B on the first photomask 21 is affected by, for example, theaberration of the projection lens 3, with the result that the alignmentmark 25A is formed as a transferred alignment mark 41 in a positiondeviated from the desired position in an amount of X1 as shown by thesolid line in FIG. 1A.

[0043] It follows that, if the alignment mark 41 is formed on the wafer1 by using a resist mask formed by developing the resist 21A that wasexposed to light, the alignment mark 41 is formed in a position deviatedfrom the position of the alignment mark 25A on the photomask 21 in anamount of X1.

[0044] Concerning the overlay inspecting mark formed in the mark portion5B on the chip 11 for inspecting the deviation of the overlay of thedevice pattern, the resist 21A is exposed to light by using aninspecting mark 5A within the inspecting mark portion 5B formed on thefirst photomask 21, as shown in the left portion of FIG. 1A. Like thealignment mark 25A, the inspecting mark 5A is also affected by, forexample, the aberration of the projection lens 3, with the result thatthe inspecting mark 5A is formed as a mark portion 42 for inspecting thedeviation of the transfer alignment in a position deviated from theideal position denoted by broken lines in an amount of X1.

[0045] To be more specific, if the mark 42 for inspecting the deviationof overlay is formed on the chip 11 by using the resist mask formed bydeveloping the resist 21A that is exposed to light, the inspecting mark42 is formed as the mark portion 41 for inspecting the deviation in aposition deviated in an amount of X1 from the ideal mark 5A formed onthe photomask 21 for inspecting the deviation of overlay, as shown inFIG. 1A. Therefore, the relative positions between the alignment mark 41or the overlay inspection mark 42 and the device pattern on the chip 11are similar to those on the photomask 21.

[0046] Incidentally, the positional deviation in the X-direction aloneis shown in FIG. 1A. However, the positional deviation caused by, forexample, the aberration of the projection lens 3 takes place not only inthe X-direction but also in the Y-direction. The positional deviation inthe X-direction alone is described herein. Needless to say, however, itis necessary to inspect the amount of the positional deviation and tocorrect the deviation in the Y-direction, too. Since the positiondeviation in the Y-direction can be corrected as in the correction ofthe positional deviation in the X-direction, description is omittedherein in respect of the correction of the positional deviation in theY-direction.

[0047] In the next step, a resist 22A newly formed on the wafer 1 byusing a second photomask 22 formed of a glass substrate 26 and a lightshielding film 27 formed on the substrate 26 is exposed to light, asshown in FIG. 1B. Formed on the second photomask 22 are a mark forinspecting the deviation of overlay together with the device pattern. Analignment mark is not formed on the second photomask 22.

[0048] The mark for inspecting the deviation of alignment formed on thesecond photomask 22 is a mark 43 for inspecting the deviation ofalignment formed inside the mark 42, as shown in FIG. 1C, unlike themark 42 for inspecting the deviation of alignment, which is formed onthe chip 11 by using the mask mark 5A for inspecting the deviation ofalignment, which is formed on the first photomask 21.

[0049] The mark 43 differs in size and shape from those of the mark 42so as to distinguish easily these marks 42 and 43. Also, the mark 43 forinspecting the deviation of alignment is formed on the wafer at aposition different from that of the mark 42. In this embodiment, themark 43 is formed inside the mark 42. However, the mark 43 may be formedoutside the mark 42.

[0050] The exposure position of the second photomask 22 is adjusted inconformity with the alignment mark 41 within the alignment mark portion25B within the chip 11 on the wafer 1 in the step of exposing the resistfilm 22A to light by using a light exposure apparatus. Therefore, thesecond photomask 22 does not require a mask pattern for the alignmentmark. However, when another alignment mark is required for alignment athird photomask, for example, this another alignment mark may be formedon the chip 11 aligned to the alignment mark formed on the chip 11 usingthe second photomask 22.

[0051] The mark 43 for inspecting the deviation of alignment, which istransferred to the chip 11 on the wafer 1 by using the second photomask22, is transferred inside the mark 42 for inspecting the deviation ofalignment, which is transferred by using the first photomask 21.

[0052] Each of the alignment mark 25A of the first photomask and themark 5A for inspecting the deviation of alignment uses at least a partof the device pattern of the first photomask 21 as it is, or use apattern equal to or similar to the device pattern. Also, the mark 43 forinspecting the deviation of alignment of the second photomask 22 issubstantially equal in size and shape to the device pattern (not shown)of the second photomask 22.

[0053] Therefore, as in the case of the first photomask 21, the devicepattern and the overlay inspection mark 43 formed on the chip 11 usingthe second photomask 22 are affected in the similar degree by theaberration and focus position of the projection lens 3 and the deviationof the device pattern is similar to the overlay inspection mark 43.

[0054] However, the deviation of the device pattern and the marks of thefirst photomask 21 formed on the chip 11 and the deviation of the devicepattern and the marks of the second photomask 22 formed on the chip 11are not the same, because the sizes and shapes of the first and secondphotomasks are not the same and because the deviation is also affectedby the mechanical errors of the exposure apparatus and a change in theexposure conditions when the first and second photomasks are used in thesame exposure apparatus.

[0055] For example, by setting the overlay inspection mark 43 to beformed at a center potion of the overlay mark 42, when the devicepatters of the first and second photomasks 21 and 22 have the similarsizes and shapes, the deviation amount of the mark 43 from the center ofthe mark 42 will show the difference of the deviation of the markscaused by the difference of the sizes and shapes of the device patternson the first and second photomasks 21 and 22, as shown in FIG. 1C.

[0056] In the first embodiment, the deviation of alignment between theresult of light exposure of the first photomask 21 and the result oflight exposure of the second photomask 22 is measured by using a markfor measuring the deviation of alignment consisting of the first mark 42for inspecting the deviation of alignment formed on the chip 11 and themark 43 for inspecting the deviation of alignment formed on the resist22A. Alternatively, the deviation of alignment noted above can bemeasured by forming each of the marks 42 and 43 on the chip 11.

[0057] For example, as shown in FIG. 1C, the difference D between thecenter C1 of the center points G1 and G2 in the outer overlay inspectionmarks 42 and the center C2 of the center points G3 and G4 in the inneroverlay inspection marks 43 is measured. This measured difference Dshows a deviation generated between the overlay inspection marks formedon the chip 11 by using the photomasks 21 and 22.

[0058] The mark 42 for inspecting the deviation of alignment is a markformed by the light exposure of the first photomask 21 and has a shapeequal to or similar to a part of the device pattern 4 included in thefirst photomask 21. On the other hand, the mark 43 for inspecting thedeviation of alignment is a mark formed by the light exposure of thesecond photomask 22 and has a shape equal to or similar to a part of thedevice pattern (not shown) included in the second photomask 22. In FIG.1C, the mark 43 for inspecting the deviation of overlay is shown in alarge shape differing from the actual shape for the sake of conveniencein the drawing. In general, however, the mark 43 is divided like themark 42 for inspecting the deviation of alignment, though it is possiblefor the marks 42 and 43 to be slightly different from each other in theshape.

[0059] Incidentally, it is possible to transfer the conventionalpatterns 101 and 102 simultaneously by using the photomasks 21 and 22for use in combination in the present invention, as shown in FIG. 1C.The mark consist of the mark 102 for inspecting the deviation ofoverlay, which is formed by using the first photomask 21, and the mark101 for inspecting the deviation of overlay, which is formed by usingthe second photomask 22.

[0060] As described above, in the first embodiment of the presentinvention, each of the alignment mark 41 and the marks 42, 43 forinspecting the deviation of overlay includes a part or a similar patternof the device pattern, with the result that these marks receive theerror caused by the influence of the aberration of the projectionoptical system such as a projection lens used in performing the patterntransfer in substantially the same degree. This implies that, since theamounts of positional deviation are the same for each of these patternsand marks, it is possible to expect the mask alignment and devicepattern overlay with a high accuracy in the following exposure steps.

[0061] A second embodiment of the present invention will now bedescribed with reference to FIGS. 2A to 2D which collectively showschematically the alignment mark and the mark for inspecting thedeviation of overlay, in a case in which are formed different patternson the same photomask.

[0062] The second embodiment is featured in that, in the case where afirst photomask and a second photomask are used in the lithography stepincluded in the manufacturing process of a semiconductor device, and thelight exposure is performed by using the first or second photomask, eachof the mark for inspecting the deviation of overlay of the devicepatterns and the alignment mark includes at least a part of the devicepattern shape included in the photomasks.

[0063] The first photomask includes first and second device patternshaving different sizes and shapes and the second photomask includes athird device pattern of a size and shape different from those of thefirst and second device patterns. Therefore, the first and secondphotomasks include the overlay inspection mark and an alignment markeach having at least a part of these first to third device patterns.

[0064] In other words, each of the alignment mark and the mark forinspecting the deviation of overlay is formed by combining differentpatterns on the same photomask. The patterns are selected from thetypical patterns within the device patterns included in the first andsecond photomasks.

[0065] In the second embodiment, a thick pattern and a fine pattern areselected from the device pattern in order to facilitate the descriptionof the present invention. These thick pattern and fine pattern arealternately arranged in the patterns of the alignment mark and the markfor inspecting the deviation of overlay. The thick pattern and the finepattern differ from each other in the amount of generation of thepositional error when these patterns are transferred onto the wafer. Itis possible to measure the positions of the thick pattern and the finepattern by subjecting the generation amount of the positional error to asignal processing.

[0066] As shown in FIG. 2A, an alignment mark consisting of a thickpattern 32 and a thin pattern 33 alternately arranged is formed in afirst photomask 31. The alignment mark is transferred onto a wafer 30 byusing these thick pattern and fine pattern. The fine pattern 33 in aposition that should originally be transferred is actually deviated inits position so as to actually allow a fine pattern 34 to be transferredin a deviated position. The rate of the positional deviation of the finepattern 33 is larger than that of the thick pattern 32. Since the thickpattern 32 and the fine pattern 33 differ from each other in the amountof the positional error in X and Y directions when transferred onto thewafer, each of the position of the thick pattern 32 and the position ofthe fine pattern 33 is measured by a signal processing in view of thedifference in the generation amount of the positional error noted above.

[0067] When an alignment mark is transferred onto the wafer 30 using thefirst photomask 31, the ideal position of the fine pattern 33 shown bythe dotted lines is deviated at the position shown by the solid lines asthe deviated fine pattern 34. The degree of the deviation of the finepattern 34 is larger than that of the thick pattern 32. In this case,the deviation of the thick pattern 32 is assumed to be substantiallyzero.

[0068] However, in fact, the deviation of the thick pattern 32 is notzero and is deviated slightly in X and Y directions. Therefore, when adistance between the transferred thick pattern 32 and the transferredthin pattern 34 is measured, the measured distance will denote a sum ofan original distance between the thick and thin patterns on thephotomask 31 and a difference between the deviation of the thick patternand the deviation of the thin pattern transferred on the wafer, or arelative deviation amount therebetween. Therefore, when the originaldistance is subtracted from the sum value, the resultant value willdenote a relative deviation amount ΔX in the X direction. In thismanner, the positional deviation amount ΔX due to the pattern differenceof the device patterns can be determined on the alignment marktransferred on the wafer.

[0069] The relative deviation amount between alignment markscorresponding to the thick pattern 32 d and thin pattern 33 d which areincluded in the device pattern in the first photomask is measured byprocessing measured signals by taking the amount ΔX into consideration.

[0070] For example, as shown in FIG. 2D, a pattern 39 d corresponding toa device pattern is transferred between the thick pattern 32 and thethin pattern 33 having an intermediate size between those of the thickand thin patterns 32 and 33 on the wafer using the second photomask. Inthis case, since the relative deviation amounts ΔX of the thick and thinpatterns 32 and 33 are known, it is easy to align the second photomaskso as to position the third pattern 39 d at the center position betweenthe thick and thin patterns 32 and 33.

[0071]FIGS. 2B and 2C show another case in which a third pattern 39 d isfirst formed on the wafer using the first photomask and then the overlayinspection marks used to transfer the thick pattern 32 d and thinpattern 33 d are formed in such a manner that the third pattern 39 d ispositioned at the center of the thick and thin patterns 32 d and 33 d,as shown in FIG. 2D.

[0072] As shown in FIGS. 2B and 2C, the overlay inspection marks in thecase where the device patterns have thick patterns, or the marks forinspecting the deviation of overlay for a large pattern comprisingreference patterns 35 and 37 are formed on the wafer using the firstphotomask 31. In the same time, the third pattern 39 d having theintermediate size is formed as shown in FIG. 2D.

[0073] In the next step, another thick pattern 36 is formed as theoverlay inspection mark inside the thick patterns 35 by the secondphotomask. The third pattern 39 d is designed to be formed at anintermediate position of the thick and thin patterns 32 d and 33 d asshown in FIG. 2D.

[0074] In the same time, inside the thick reference patterns 37 thinpattern 38 for the overlay inspection mark is formed using the secondphotomask as shown in FIG. 2C.

[0075] The mark for inspecting the deviation of alignment for a smallpattern comprises a thick pattern 37 formed of the first photomask and afine pattern 38 formed of the second photomask.

[0076] In this case, the overlay error in the case where the devicepattern has a thick pattern can be measured using the overlay inspectionmarks 35 and 36 shown in FIG. 2B, and the overlay error in the case ofthin device pattern can be measured using the overlay inspection marks37 and 38 shown in FIG. 2C.

[0077] When an overlay inspection mark for the large pattern and anoverlay inspection mark for the small pattern are prepared on the firstand second photomasks, the overlay inspection for the respective devicepatterns can be performed. Therefore, as shown in FIG. 2D, it is easy toform the thick pattern 32 d and the thin pattern 33 d using the secondphotomask with respect to the device pattern 39 d of the intermediatesize using the first photomask at a correct position.

[0078] A third embodiment of the present invention will now be describedwith reference to FIGS. 3A to 3C. Specifically, FIGS. 3A to 3Ccollectively show schematically the marks for inspecting the deviationof alignment each formed on the photomask.

[0079] In the third embodiment, first and second sets of overlayinspection marks are formed using the first and second photomasks. Thefirst set of overlay inspection marks are prepared for measuring a firsterror denoting mainly a mechanical error caused by the exposureapparatus, which does not include an error due to the aberration of theprojection lens. The second set of overlay inspection marks are preparedfor measuring a second error mainly caused by the exposure error due tothe projection lens.

[0080] When an overlay exposure using a second photomask is performed onthe pattern formed on the chip using a first photomask, the overlay ofthe second photomask is adjusted by taking the first and second errorsinto consideration, thereby achieving a desired accuracy of the patternoverlay.

[0081] In this case, it is possible to use an alignment mark equal tothat used in the first embodiment shown in FIG. 1A and the marks shownin FIGS. 3A to 3C as marks for inspecting the deviation of overlay inthe case where the light exposure is performed by using the firstphotomask and the second photomask. The transferred patterns in the stepof the light exposure performed by using the first photomask are theoutside patterns 61 shown in FIG. 3A, a thick frame-like referencepattern 64 of a rectangular shape and the overlay inspection mark 63having a device pattern as shown in FIG. 3B.

[0082] The patterns transferred in the light exposure step using thesecond photomask are an inside pattern 62 shown in FIG. 3A, a thickframe-like reference pattern 65 having a rectangular shape as shown inFIG. 3C, and the overlay inspection mark 66 having a device pattern asshown in FIG. 3C.

[0083] First, using the reference pattern 64 and the pattern 63 havingthe device pattern shape, a relative deviation amount ΔX1 caused by theexposure by using the first photomask is measured.

[0084] For example, the measured value ΔX1 can be obtained on the basisof the distance between a inside line of the reference pattern 64 in theX direction and the side of the pattern 63 in the X direction in FIG.3B.

[0085] On the other hand, as shown in FIG. 3C, a reference pattern 65and a pattern 66 having the device pattern shape in the second photomaskare formed in the second photomask in the same manner as the patterns 63and 64 formed in the first photomask. The positional deviation amount inthe X direction between the two kinds of patterns such as the referencepattern 65 and the pattern 66 representing the device pattern is alsomeasured in the second photomask. The measured deviation is denoted asΔX as shown in FIG. 3C.

[0086] Further, the positional deviation amount between the firstphotomask and the second photomask measured by the conventional marks 61and 62 is measured as ΔX12. The ΔX12 may be measured as a distancebetween a side line of the outside pattern 61 and a corresponding sideline of the inside pattern 62 facing the outside pattern 61.

[0087] The positional deviation amount ΔX12D between the device patterntransferred by the first photomask and the device pattern transferred bythe second photomask can be obtained from these three measured values bythe formula given below:

ΔX12D:ΔX12+ΔX1+ΔX2

[0088] It is possible to obtain a high overlay accuracy by making thevalue of ΔX12D to be zero in the next light exposure step using theoverlaid masks.

[0089] Also, in the third embodiment shown in FIGS. 3B and 3C, the foursides of the overlay inspection marks 63 and 66 having the devicepattern shape is surrounded by the reference marks 64 and 65. However,the present invention is not limited to the particular construction. Forexample, it is possible to have only two sides in the X and Y directionsof the overlay inspection mark 63 surrounded by the reference mark 64.

[0090] It is also possible to arrange the inspection marks with areference pattern sandwiched therebetween. Further, it is possible toarrange the reference pattern simply within a measuring region in thevicinity of the device pattern.

[0091] A fourth embodiment of the present invention will now bedescribed with reference to FIGS. 4, 5A and 5B. FIG. 4 schematicallyshows an alignment mark formed by combination of different patterns onthe same photomask. On the other hand, FIGS. 5A and 5B collectively showschematically a mark for inspecting the deviation of overlay formed bythe combination of different patterns on the same photomask.

[0092] The fourth embodiment covers the case where a first photomask anda second photomask are used in the lithography steps included in themanufacturing process of a semiconductor device, and is featured inthat, when the light exposure is performed by using the first or secondphotomask, a mark for inspecting the deviation of overlay of thephotomask and an alignment mark are constructed to include at least apart of the device pattern included in the photomask, and that analignment mark and a mark for inspecting the deviation of overlay areformed by the combination of different patterns on the same photomask.

[0093] However, in the case of using the alignment mark and the mark forinspecting the deviation of overlay as shown in, for examples, FIGS. 2Ato 2C, the length in the longitudinal direction is rendered very largecompared with the device pattern, even if the pattern size in the widthdirection corresponds to the device pattern. In such a case, there is apossibility of occurring an inconvenience that is not expected in thedevice pattern to take place in the process of consecutively executingthese marks.

[0094] For example, a problem is generated in respect of the dependenceof the dicing on the pattern in the CMP process, making it necessary toshorten the length of the mark. Under the circumstances, the alignmentmark is divided for use as shown in FIG. 4. Also, the mark forinspecting the deviation of overlay is also divided as shown in FIGS. 5Aand 5B. To be more specific, each of the fine patterns and the thickpatterns is divided into a plurality of small patterns.

[0095] As shown in FIG. 4, an alignment mark consisting of a thickpattern 42 and a fine pattern 43 is formed on the first photomask 41.The alignment mark is transferred onto the wafer by using the particularalignment mark formed on the first photomask 41. The fine pattern in aposition that should originally be transferred is actually deviated inits position so as to actually allow a fine pattern to be transferred ina deviated position. The rate of the positional deviation of the finepattern is larger than that of the thick pattern. Since the thickpattern and the fine pattern differ from each other in the amount of thepositional error when transferred onto the wafer, each of the positionof the thick pattern and the position of the fine pattern is measured bya signal processing in view of the difference in the generation amountof the positional error noted above.

[0096] Also, as shown in FIGS. SA and 5B, when it comes to the mark forinspecting the deviation of alignment formed on the wafer, the mark forinspecting the deviation of overlay for a large pattern comprises athick pattern 45 formed of the first photomask and another thick pattern46 formed of the second photomask. On the other hand, the mark forinspecting the deviation of overlay for a small pattern comprises athick pattern 47 formed of the first photomask and a fine pattern 48formed of the second photomask.

[0097] If the marks for inspecting the deviation of overlay are preparedfor the large pattern and the small pattern, respectively, as describedabove, it is possible to measure the deviation of alignment relative toeach of these large and small patterns. The reference patterns 64 and 65shown in FIGS. 3B and 3C can also be divided for use as in the thirdembodiment. With the particular construction, it is possible to measurethe deviation of alignment for each of the patterns.

[0098] A fifth embodiment of the present invention will now be describedwith reference to FIGS. 6A to 6E, which are cross sectional viewscollectively showing the manufacturing process of a semiconductordevice. Described in the following is manufacturing steps of asemiconductor device by employing the alignment method of the presentinvention.

[0099] In the first step, a silicon oxide (SiO₂) film 73 is formed on asemiconductor substrate 70 such as a silicon semiconductor substrate,followed by forming a photoresist film 74 on the silicon oxide film 73,as shown in FIG. 6A. Further, the photoresist film 74 is selectivelyexposed to light by using a first photomask 71 described previously inconjunction with the first to fourth embodiments, followed by thedeveloping treatment to form open portions.

[0100] Then, the silicon oxide film 73 is etched with the photoresist 74used as a mask so as to form contact holes in the silicon oxide film 73,followed by forming a first layer aluminum wiring 75 on the siliconoxide film 73, as shown in FIG. 6B. The first layer aluminum wiring 75is electrically connected to the semiconductor substrate 70 via thecontact holes.

[0101] In the next step, a silicon oxide (SiO₂) film 76 is formed in amanner to cover the upper surface of the first layer aluminum wiring 75,followed by planarizing the surface of the silicon oxide film 76 by CMP,as shown in FIG. 6C.

[0102] Then, a photoresist film 77 is formed on the silicon oxide film76. The photoresist film 77 is then selectively exposed to light byusing a second photomask 72 of the construction equal to that describedpreviously in conjunction with the first to fourth embodiments so as toform an open portion, as shown in FIG. 6D. Then, the silicon oxide film76 is etched with the photoresist film 77 used as a mask so as to form acontact hole in the silicon oxide film 76.

[0103] After removal of the photoresist film 77, a second layer aluminumwiring 78 is formed on the silicon oxide film 76, followed by patterningthe second layer aluminum wiring 78. The second layer aluminum wiring 78is electrically connected to the first layer aluminum wiring 75 via thecontact hole, as shown in FIG. 6E.

[0104] In the manufacturing process described above, each of the firstand second photomasks is constructed such that each of the alignmentmark and the mark for inspecting the deviation of overlay includes apart of the device pattern or an equivalent pattern as in the firstembodiment. It follows that the alignment mark and the mark forinspecting the deviation of overlay receive the error caused by theinfluence given by the aberration of the projection optical systemincluding a projection lens used in performing the pattern transfer insubstantially the same degree. As a result, the amount of the positionaldeviation of the pattern is the same, making it possible to achieve analignment of a high accuracy, i.e., formation of the device pattern.

[0105]FIG. 7 schematically shows that a large number of chips 11 areformed on the wafer 1 such as a silicon wafer. The chips 11 are arrangedon the wafer 1 to form a two dimensional array, and dicing lines 12 areformed between the adjacent chips 11. After the processing of the wafer1, the wafer 1 is cut along the dicing lines 12 so as to obtain aplurality of the individual chips 11.

[0106] The alignment mark and the mark for inspecting the deviation ofoverlay referred to in each of the first to fourth embodiments of thepresent invention described above are constructed as follows:

[0107] (1) These marks can be formed on the dicing lines.

[0108] (2) These marks can be formed in positions close to the devicepattern on each chip.

[0109] (3) The device pattern formed in a selected single chip can beused as an alignment mark and a mark for inspecting the deviation ofoverlay in the subsequent lithography step.

[0110] Since each of the alignment mark and the mark for inspecting thedeviation of overlay includes a part of the device pattern or anequivalent pattern, these marks receive an error caused by the influencegiven by the aberration of the projection optical system used inperforming the pattern transfer in substantially the same degree as thedevice pattern. This implies that the positional deviation amount ofthese patterns is the same, with the result that it is possible toexpect an alignment of a high accuracy. It is also possible to performthe measurement with a high accuracy in measuring the error in theoverlay. It should also be noted that, in the case of including aplurality of patterns differing from each other in the size and shape ofthe device pattern, it is possible to achieve an alignment of a highaccuracy even if the positional deviation amount caused by, for example,the aberration of the projection optical system differs depending on thepattern.

[0111] What should also be noted is that it is possible to expect analignment of a high accuracy by measuring the positional deviationamount of the device pattern of the first photomask and the secondphotomask, the deviation being caused by, for example, the aberration ofthe projection optical system, and by using the result of themeasurement for the correction of the position in performing the lightexposure by using the first photomask and second photomask which areoverlaid one upon the other.

[0112] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. An alignment method, comprising: forming at leasta first device pattern and an alignment mark on a wafer, using a firstphotomask having the first device pattern and the alignment mark whichhas a shape equal to or similar to that of said first device pattern;and positioning a second photomask with respect to a resist film formedon said wafer according to said alignment mark formed on said wafer. 2.An alignment method according to claim 1 , further comprising: formingon said wafer a first deviation inspection mark together with said firstdevice pattern and said alignment mark, using said first photomaskhaving the first deviation inspection mark in addition to the firstdevice pattern and the alignment mark; positioning said second photomaskwith respect to the alignment mark and the first deviation inspectionmark formed on said wafer, said second photomask having a second devicepattern and a second deviation inspection mark which has a shape equalto or similar to that of said second device pattern; and forming, at aposition on said resist film corresponding to said first deviationinspection mark, an exposure pattern of said second deviation inspectionmark, together with said second device pattern.
 3. An alignment methodaccording to claim 1 , further comprising: forming the alignment markand the first device pattern on the wafer by using the first photomaskhaving the first device pattern including first and second devicepattern elements with different sizes and shapes and alignment markincluding first and second alignment mark elements with sizes and shapescorresponding to those of the first and second device pattern elements;and positioning said second photomask with respect to said waferaccording to positions of said first and second alignment mark elementsof the alignment mark.
 4. An alignment method according to claim 3 ,wherein said first alignment mark element has a size and a shape tocause an exposure position deviation amount due to an optical system ofan exposure apparatus for exposing the resist film being smaller thanthat caused by said second alignment mark element.
 5. An alignmentmethod according to claim 2 , wherein said first photomask has first andsecond deviation inspection reference marks having similar size andshape with each other; and said second photomask has a first inspectionmark with a size and shape similar to said first deviation inspectionreference mark, the first inspection mark being positioned on said waferin association with said first deviation inspection reference mark, andhas a second inspection mark causing an exposure deviation amount due toan optical system of an exposure apparatus used for exposing said resistfilm larger than that of said first inspection mark, the secondinspection mark being positioned on said wafer in association with saidsecond deviation inspection reference mark; and the alignment methodfurther comprising: correcting the exposure positions of the first andsecond photomasks using selectively one of a first arrangement or asecond arrangement according to the size and shape of the device patternformed in said second photomask, the first arrangement being acombination of said first deviation inspection reference mark and saidfirst inspection mark and the second arrangement being a combination ofsaid second deviation inspection reference mark and said secondinspection mark.
 6. An alignment method according to claim 2 , whereinsaid first photomask has a first deviation inspection mark, a firstreference mark, and a second deviation inspection mark which has a sizeand a shape equal to or similar to said first device pattern deviatedlargely caused by the optical system of an exposure apparatus withrespect to the first reference pattern; and said second photomask has asecond reference mark, a third deviation inspection mark which has asize and a shape equal to or similar to said second device patterndeviated largely caused by the optical system of the exposure apparatuswith respect to the second reference pattern, and a fourth inspectionmark positioned in association with the first deviation inspection markformed on said wafer; and the alignment method further comprising:calculating a sum of a first deviation between said first and fourthdeviation inspection marks, a second deviation between said firstreference pattern and said second deviation inspection mark, and a thirddeviation between said second reference pattern and said third deviationinspection; and correcting an exposure position of another photomaskusing the calculated sum.
 7. An overlay inspection method for aphotomask, comprising: forming on a wafer a first device pattern and analignment mark, using a first photomask having at least the first devicepattern and the alignment mark which has a shape equal to or similar tothe first device pattern; exposing said resist film formed on the waferto the second photomask according to the alignment mark; and determiningthe positioning accuracy of the second photomask with respect to thewafer using the alignment mark.
 8. An overlay inspection methodaccording to claim 7 , further comprising: forming on said wafer a firstdeviation inspection mark together with said first device pattern andsaid alignment mark, using said first photomask having the firstdeviation inspection mark in addition to the first device pattern andthe alignment mark; positioning said second photomask with respect tothe alignment mark and the first deviation inspection mark formed onsaid wafer, said second photomask having a second device pattern and asecond deviation inspection mark which has a shape equal to or similarto that of said second device pattern; and forming, at a position onsaid resist film corresponding to said first deviation inspection mark,an exposure pattern of said second deviation inspection mark, togetherwith said second device pattern.
 9. An overlay inspection methodaccording to claim 7 , further comprising: forming the alignment markand the first device pattern on the wafer by using the first photomaskhaving the first device pattern including first and second devicepattern elements with different sizes and shapes and alignment markincluding first and second alignment mark elements with sizes and shapescorresponding to those of the first and second device pattern elements;and positioning said second photomask with respect to said waferaccording to positions of said first and second alignment mark elementsof the alignment mark.
 10. An overlay inspection method according toclaim 9 , wherein said first alignment mark element has a size and ashape to cause an exposure position deviation amount due to an opticalsystem of an exposure apparatus for exposing the resist film beingsmaller than that caused by said second alignment mark.
 11. An overlayinspection method according to claim 8 , said first photomask has firstand second deviation inspection reference marks having similar size andshape with each other; and said second photomask has a first inspectionmark with a size and shape similar to said first deviation inspectionreference mark, the first inspection mark being positioned on said waferin association with said first deviation inspection reference mark, andhas a second inspection mark causing an exposure deviation amount due toan optical system of an exposure apparatus used for exposing said resistfilm larger than that of said first inspection mark, the secondinspection mark being positioned on said wafer in association with saidsecond deviation inspection reference mark; and the overlay inspectionmethod further comprising: correcting the exposure positions of thefirst and second photomasks using selectively one of a first arrangementor a second arrangement according to the size and shape of the devicepattern formed in said second photomask, the first arrangement being acombination of said first deviation inspection reference mark and saidfirst inspection mark and the second arrangement being a combination ofsaid second deviation inspection reference mark and said secondinspection mark.
 12. An overlay inspection method according to claim 8 ,wherein said first photomask has a first deviation inspection mark, afirst reference mark, and a second deviation inspection mark which has asize and a shape equal to or similar to said first device patterndeviated largely caused by the optical system of an exposure apparatuswith respect to the first reference pattern; and said second photomaskhas a second reference mark, a third deviation inspection mark which hasa size and a shape equal to or similar to said second device patterndeviated largely caused by the optical system of the exposure apparatuswith respect to the second reference pattern, and a fourth inspectionmark positioned in association with the first deviation inspection markformed on said wafer; and the overlay inspection method furthercomprising: calculating a sum of a first deviation between said firstand fourth deviation inspection marks, a second deviation between saidfirst reference pattern and said second deviation inspection mark, and athird deviation between said second reference pattern and said thirddeviation inspection; and correcting an exposure position of anotherphotomask using the calculated sum.
 13. A photomask comprising: a devicepattern; an alignment mark having a size and a shape equal to or similarto those of said device pattern; and a deviation inspection mark havinga size and a shape equal to or similar to those of said device pattern.14. A photomask comprising: a device pattern configuration including atleast two device patterns having different sizes and shapes; analignment mark including at least two alignment mark elements havingdifferent sizes and shapes corresponding to those of the devicepatterns; and a deviation inspection mark having a shape including apart of said device pattern configuration.
 15. A photomask comprising: adevice pattern configuration; an alignment mark including a referencepattern and a part of said device pattern configuration; and a deviationinspection mark having a shape including a part of said device patternconfiguration.
 16. A photomask according to any one of claims 8 to 15 ,wherein said alignment mark and said deviation inspection markrespectively have a width and a length corresponding to those of saiddevice pattern configuration.